Ever since the use of implantable devices, its permanent access has been an issue. There are several problems from sending or retrieving data to how to power such devices. For instance, a surgery to replace batteries from neuro-prostheses or pacemakers would be avoided if direct connection to the devices would be possible. Different component such as electrodes, biosensors or more complex electronic devices to measure different biological parameters would benefit from a direct connection to out of the body devices such as stimulators, recorders, robotic prosthesis, etc. A stimulator could be used from outside to body for pain treatment by sending electric impulses to implanted electrodes if such link would be safe and permanently available.
A Human-Machine-Gateway (HMG) is, for example, required for achieving a natural control of a robotic prosthesis. “Natural” herein is referred to as produce control in the same way that an intact physiological system. This means coordinated and simultaneous movements of different degrees of freedom. Furthermore, “natural” also implies that the input signals must come from muscles that originally are meant to produce the intended movement or/and from nerves that controlled those muscles. Fine movements performed by actuators in the robotic prosthesis require a long-term stable and defined connection to the human body that provides input control signals.
Accordingly, a bone anchored robotic prosthesis may be fixed on an amputation stump of a limb by an implant (fixture) which is implanted in a bone inside the stump. Accordingly, bone anchored prosthesis are attached directly to the bone and not attached to the body via the skin of the stump.
The fixture may preferably be implanted into the bone based on the principle of osseointegration. Osseointegration implies direct contact between the fixture and the bone. That means the fixture as the anchoring element is surgically inserted into the bone of the amputation stump. After approximately six months a skin penetrating connection component (abutment) is attached to the fixture. Then, the patient's prosthesis is attached to the outer part of the abutment.
For a natural control of the bone anchored robotic prosthesis several further components are required. For example, input and output signals may be generated and transmitted to actuators and from sensors in the robotic prosthesis and to electrodes inside the limb. The required nerve and/or muscle signals as the control input are detected by biosensors, for example, nerve electrodes or muscle electrodes, and transmitted to a control circuit or amplifier located inside the robotic prosthesis or the limb itself. Furthermore, signals from the robotic prosthesis are processed in a control circuit and feedback to the patient. Therefore, the user of such a robotic prosthesis may naturally control the actuators provided in the robotic prosthesis in accordance to the signals detected in the electrodes and used the feedback sent from the prosthesis for a close loop control.
The lack of good algorithm and control systems were once the principal issues for accomplishing a complex prostheses control. Nowadays several researches have shown that it is possible to identify fingers and hand positions using different pattern recognition algorithms such as artificial neural networks (ANNs), support vector machines (SVM), hidden markov models (HMM), wavelets, etc. Manipulation of different devices like robotic arms using myoelectric signals as information source and SMV as control algorithm has been proved as a feasible technology as well. However, these examples and all known experiments have been short-term implementations.
Now that pattern recognition algorithms and hardware for a real time control are available, the major issue is the long-term stability of the biosignals. The stability is heavily related on how the biosignals are acquired which brings in other two major problems. The first one is the amount of signals that are possible to retrieve due the physical limitations. The second problem is related to how natural it would be for the patient to produce signals for a given propose.
The following are some of the issues in a practical implementation of a prosthetic control based in pattern recognition algorithms. These problems are mostly attributed to the surface electrodes.                Electrodes cannot remain placed indefinitely due to skin related issues.        Electrodes cannot be placed consistently in the same spot after removing the prosthesis.        A different placement of the electrode will required a retraining of the control system.        The signal changes dramatically with the environmental conditions, i.e. sweating.        Artefacts are very easily generated due to limb movement and electrode liftoff.        A patient needs to have a minimum level of myoelectric signals to become a candidate for using a myoelectric prosthesis. This is not always the case depending on the amputation level and the muscle surface left for the electrodes placement.        A wide limb surface area needs to be covered to have enough control signals.        Muscle imbalance could be created if the electrodes are wrongly placed resulting in muscles being more exercised than others. In the long run, this will cause that the big muscle's signal masks the other one. Muscle imbalance can also cause prosthesis socket instability.        Clinical studies have shown that acceptance of prostheses is difficult to achieve, especially the myoelectric type where there are more possibilities of failure.        Lack of feedback to the patient.        Unnatural control. The same group of muscles control different units in a sequential manner instead of individual muscles controlling specific actions simultaneously.        
EP 0 595 782 B1 discloses an anchoring element (fixture) for supporting a prosthesis, said anchoring element having essentially the form a screw and being arranged for a connection by its outer end portion to said prosthesis and by its opposite inner end portion to be inserted and anchored in bone tissue.
WO 03/000161 A1 discloses a system of implantable sensor/stimulation devices that is configured to communicate with a prosthetic device, e.g., an artificial limb, via a wireless communication link, preferably bidirectional. By communicating between the implantable devices coupled to neural pathways within a human and motor/sensor interfaces in the prosthetic device, a machine and a human/machine interface is established to replace an absent limb.
GB 2 445 869 A discloses a percutaneous prosthetic device comprising at least one soft tissue fixture adapted to be fixed to the musculotendinous soft tissue of a residual limb and a percutaneous anchor for an external prosthesis that is fixedly coupled directly or indirectly, to the bone of the residual limb in use, the percutaneous anchor having a percutaneous sleeve component. Furthermore, the device comprises at least one transmission means allowing transmission of one or more signals between the soft tissue fixture and external prostheses. The transmission means is guided outside the bone through the percutaneous anchor to the external prosthesis. The signal or signals relate to contraction and/or relaxation of muscle in the residual limb and do not consider signals form nerves. Preferably the transmission means comprises a connecting means connecting the soft tissue fixture and an external prosthesis in use. The connecting means may comprise a mechanical or an electrical connector. Preferably the connecting means comprises a seal connection within the percutaneous component to provide an effective barrier between the internal and external environment.
CN 1545988 discloses a method for controlling a prosthesis by means of biological electrical signals in human bodies. Accordingly, an upper end of an implantation member is inserted into a remnant bone of an amputee's stump. The implantation member comprises a hole located in a portion of the implantation member being not implanted into the bone, the hole comprising an inner end exiting into the soft tissue. Afterwards, the steps of connecting the lower projecting member with a artificial limb, implanting the electrodes into the nerve-tract or muscle hank in the soft tissue, leading the contact conductor to the external signal conditioning device through the through-hole of the not implanted portion of the implantation member, carrying out magnification and filtration to the signal collected by the electrodes, mapping the signal into the control message for artificial limb motion, the control signal feeding to the motor to drive the artificial limb, are performed.
U.S. Pat. No. 6,034,295 discloses an implantable device, such as a femoral head prostheses, with a body of biocompatible material shaped to suit its medical function, which forms in internal cavity and has open apertures that lead from the cavity to the outside. The cavity serves to receive biological material into which the tissue that surrounds the implanted device is intended to grove through the apertures. The device is provided with at least two electrodes, at least one of which is located in the cavities based apart from the inside of the body that forms the cavity. The electrodes are provided with an arrangement for supplying a low frequency alternating voltage, so that by means of the supplied voltage a low frequency electrical alternating field and a low frequency alternating current, whereby the tissue grow is promoted, are created inside the cavity.
FR2802083 discloses an implantable device to anchor natural or prosthetic ligaments. It is a fully implanted device with an inside cavity to secure the prosthetic ligament. The implant is used to keep the graft in place and it is especially designed for the knee articulation.